Electrolytic method of manufacturing hydrodimer of acrylonitrile



United States Patent 3,497,429 ELECTROLYTIC METHOD OF MANUFACTURINGHYDRODIMER 0F ACRYLONITRILE Kazuhiko Mihara and Maomi Seko, Tokyo,Shinsaku Ogawa and Shoichiro Kumazaki, Yokohama, and Ryozo Komori andMuneo Yoshida, Kawasaki, Japan, assignors to Asalii Kasei KogyoKabushiki Kaisha, Osaka, Japan No Drawing. Filed Nov. 28, 1966, Ser. No.597,207 Claims priority, application Japan, Dec. 3, 1965, 40/ 73,996;Dec. 13, 1965, 40/76,315 Int. Cl. B01k 3/00, 1/00 US. Cl. 204-73 7Claims ABSTRACT OF THE DISCLOSURE In the manufacture of adiponitrile byelectrolyzing in a divided cell the catholyte of an aqueous solutioncomprising acrylonitrile and a quaternary ammonium sulfate, usingsulfuric acid solution as an anolyte, the improvement comprising using aconcentration of dissolved acrylonitrile in said catholyte of from 3 to10% by weight.

This invention relates to a method for the manufacture of adiponitrile,the hydrodimer of acrylonitrile, characterized by electrolyzing acatholyte comprising an aqueous solution of alkyl, aryl or aralkylquaternary ammonium sulfate and acrylonitrile in a divided cell,employing an anolyte of an aqueous solution of sulfuric acid and theanolyte being separated, by a cation-exchange membrane placed betweenthe cathode compartment and the anode compartment, from the catholyte.

More particularly, it relates to a method for hydrodimerizingacrylonitrile by electrolyzing the catholyte comprising said quaternaryammonium sulfate used as the supporting electrolyte and acrylonitrile,which is characterized by separating a cathode efiluent solution intotwo phases, i.e. aqueous and oil phases by adding acrylonitrile theretoand extracting adiponitrile from the resulting aqeuous solution phase.

Particularly, this invention relates to a method for electrolyticallyhydrodimerizing acrylonitrile to adiponitrile by using quaternaryammonium sulfate with can alkyl radical having no more than three carbonatoms bonded to nitrogen atom of quaternary ammonium as a supportingelectrolyte, and electrolyzing the catholyte in which acrylonitrile isdissolved together with said supporting electrolyte. Thus, theelectrolysis of this invention may be carried out advantageously in ahigh selectivity of adiponitrile even when the acrylonitrileconcentration in the catholyte is as low as 3 to 10% by weight. In otherwords, even if the solubility of acrylonitrile in the catholyte issubstantially the same as that in water and the concentration ofacrylonitrile in the catholyte is below 10% at normal temperature, ahigh selectivity of adiponitrile may be obtained according to the methodof this invention. This is the point which is essentially different fromthe processes of conventional hydrodimerization known heretofore.

A conventional method known to the trade is of such principle that anaqueous solution containing such salt as aryl-or alkaryl sulfonate oralkylsulfate of aliphatic amine or heterocyclic amine together withacrylonitrile is contacted with the cathode and electrolyzed to obtainhydrodimerization product of acrylonitrile. Further details of thismethod are found in US. Patents Nos. 3,193,481, 3,193,480 and 3,193,477.Basic invention of these known in the literature is that by increasingthe solubility of acrylonitrile by the use of specific supporting salts,high selectivity of adiponitrile may be obtained. Such typical 3,497,429Patented Feb. 24, 1970 salts for this method are tetraethylammoniumparatoluenesulfonate or tetraethylammonium ethylsulfate. On the otherhand, Journal of the Electrochemical Society, vol. 102 (1955), page 239describes the observation that the electrolysis of the aqueous solutionof an olefinic compound, whn electrolyzed with tetraalkyl halide as thesupporting electrolyte (which is defined as the salt that keepsdischarge potential at the cathode enough negative for electrolysis),produces hydrodimer. The use of tetraalkylammonium halide for theproduction of hydrodimer of acrylonitrile has been also known from thespecification of Belgium Pat. No. 649,625.

The specification of US. Patent No. 3,193,481 describes the possible useof tetraethylammonium sulfate as a supporting salt for hydrodimerizationof acrylonitrile, however, the use of this salt is restricted for theconcentration of acrylonitrile of catholyte to at least 15% as describedat column 10 of the specification of US. Patent No. 3,193,481. Moreover,as the solubility of acrylonitrile in the catholyte by the use oftetraethylammonium sulfate will never be increased substantially morethan that in water in the range of the concentration oftetraethylammonium sulfate less than 60%, the use of tetraethylammoniumsulfate as a supporting salt is opp site to the basic idea of said US.Patent No. 3,193,481 that the increase of the concentration ofacrylonitrile in the catholyte is essentially for the good yield ofadiponitrile.

It is an object of this invention to provide a novel method for themanufacture of adiponitrile by electrolytically hydrodimerizingacrylonitrile.

Further objects and appending features of this invention will becomeapparent as the description of this specification proceeds.

According to the present invention there is provided a novel method forelectrolytically hydrodimerizing acrylonitrile to produce adiponitrileefiiciently and economically in a good stability.

This invention is essentially different from said conventionally knownmethods in that it conducts electrolysis by using as the catholyte theaqueous solution containing alkyl, aryl and/ or alkaryl quaternaryammonium sulfate and acrylonitrile, and the concentration ofacrylonitrile is substantially less than the solubility of acrylonitrilein water.

The advantages of the method of this invention may be explained morefully in the following:

The first advantage of the method of this invention consists in the useof the supporting electrolyte to facilitate the separation of the mixedsolution of adiponitrile and acrylonitrile from the aqueous solution ofsupporting electrolyte and, as a result, when the effluent solution ofthe cathode compartment is separated into the supporting electrolyte,adiponitrile, acrylonitrile and Water so as to isolate adiponitrile asthe product, the recovery of acrylonitrile and the supportingelectrolyte can be conducted very easily and re-used as the catholytecomponents.

By contrast, when tetraethylammonium p-toluenesulfonate ortetraethylammonium ethylsulfate is used as the supporting electrolyteaccording to the above known literature, acrylonitrile is dissolved to avery high concentration or at any indefinite ratio into the aqueoussolution of supporting salt, due to the existence of alkaryl sulfonateions or alkylsulfate ions as the anion. Thus, since the supportingelectrolyte dissolves acrylonitrile to very high solubility in bothwater and organic substances, it is ditfuclt to separate the organiccomponents containing adiponitrile and acrylonitrile (oil phase) fromthe aqueous solution of supporting electrolyte (aqueous phase).Moreover, even if the oil phase is separated from the water phase, thesupporting electrolyte is contained in a considerably high concentrationin the oil phase, and also adiponitrile and acrylonitrile is left in theaqueous phase. Thus, it is very difiicult to isolate adiponitrileefficiently from the oil phase. In addition, when adiponitrile andacrylonitrile are separated from the oil phase, the oil phase solutioncontaining supporting the electrolyte must be subjected to fractionaldistillation, therefore, the yield of adiponitrile is low. Besides, suchoperation involves decomposition of expensive supporting electrolyte andloss of the electrolyte at the bottom of the distillator. Also, at thetime of recovering the supporting electrolyte from the aqueous phaseafter the process of extraction by adding acrylonitrile, the fact thatadiponitrile or acrylonitrile is contained in the aqueous phase at arelatively high concentration complicates the process of separating thesupporting electrolyte and reduces the efficiency for the recovery ofthe supporting electrolyte.

However, because this invention uses said tetraammonium sulfate as thesupporting electrolyte, the solubility of acrylonitrile and adiponitrilein the aqueous solution of the supporting electrolyte is substantiallysame as that in water and much lower than that of acrylonitrile usingthe supporting electrolyte of US. Patents Nos. 3,193,481, 3,193,480 and3,193,477. Because of this lower solubility of acrylonitrile, thequaternary ammonium sulfate of this invention is convenient for theseparation of the oil phase from the aqueous phase in the effluent ofthe cathode compartment. Compared with quaternary ammonium aryl oralkaryl sulfonate or alkylsulfate used as the supporting electrolyte inthe conventional known methods, the supporting electrolyte of thisinvention has such characteristics that it is very easy to separate theoil phase of adiponitrile and acrylonitrile containing substantiallynegligible amount of supporting electrolyte from the aqueous phasecomposed of the aqueous solution of mainly supporting salt and having alow adiponitrile content. The isolation of the ingredients in the oilphase and the aqueous phase is generally accomplished by conventionalseparation or extraction method, such as cooling, heating and fractionaldistillation or the solvent extraction by use of either organic orinorganic solvent. In any form of such separating operation, because thesupporting electrolyte of this invention has little affinity and lowsolubility with and in the organic components, it is easy to separatethe organic components from the cathode effluent solution.

The second advantage of this invention consists in the fact that becausequaternary ammonium sulfate is used in the catholyte, sulfuric acidsolution as the anolyte and the electrolysis is conducted in a dividedcell separated by cation-exchange membrane placed between the cathodecompartment and the anode compartment, the anions which can migrate fromthe cathode compartment to the anode compartment are sulfate ions whichare identical with the anions existing from the beginning of theoperation in the anode compartment. Therefore, even if the constituentsof the anode compartment pass through the membrane due to the migrationby electric current or diffusion, no difficulty such as erosion of anodeoccurs. If, as in the case of the conventional known method, quaternaryammonium halide is used as the supporting electrolyte in the catholyte,the chloride ion pass through the cation exchange membrane, produceshalogen at the anode and consequently corrodes the anode, impeding itsindustrial application. Similarly, when tetraethylammoniump-toluenesulfonate is used as a.- supporting salt as in the method ofUS. Patent No. 3,193,481, p-toluenesulfonate ions move from the cathodecompartment to the anode compartment and discharge at the anode. Anodeis usually made of lead, lead alloy, or platinum, and particularly leadalloy for industrial purposes. The lead alloy is corroded by thedischarge of halide ion and sulfonic acid ion, whereas no such corrosiontakes place at all where sulfate ion discharges at the anode.

The third advantage of this invention consists in the fact that becausethe process for manufacturing quaternary ammonium sulfate is simple, andthe supporting electrolyte of this invention can be manufactured lessexpensively than the conventional known tetraethylarnmoniump-toluenesulfonate. Moreover, the rate of the Hotfman decompositionreaction of quaternary ammonium sulfate is less than that of theconventional salt such as quaternary ammonium arylsulfonate orquaternary ammonium alkylsulfate, if the alkyl groups of quaternaryammonium salt is same.

The fourth advantage of this invention consists in the fact thatadiponitrile can be manufactured in a high yield from acrylonitrilewithout having a substantial yield of propionitrile even when theacrylonitrile concentration in the electrolyte is below 10%, especiallyif quaternary ammonium sulfate in which alkyl radical having a smallnumber of carbon atoms, particularly not more than three carbon atoms isbonded to nitrogen atom, is used as the supporting electrolyte. Becausein this case solubility of acrylonitrile in the electrolyte never isincreased more than that in water in the concentration of salt less than60%. The reason for this is explained as follows: generally, the bestyield of adiponitrile is obtained in the suitable range of C/Cpreferably from 0.4 to 1, wherein C is the solubility of acrylonitrile1n the electrolyte, and C is the concentration of acrylonitrile in theelectrolyte. In this invention, C/C can be eas1ly adjusted because the Cusing quaternary ammonium sulfate is smaller than 10%. On the contrary,according to such methods as described in US. Patent No. 3,193,477 andUS. Patent No. 3,193,481, however, because the solubility ofacrylonitrile in the electrolyte C is high and, as a result, the ratioof acrylonitrile concentration (C) to the solubility (C becomes toosmall, and therefore, in such form of electrolysis, the selectivity ofadiponitrile is reduced with the increasing deviation from the suitablevalue of ratio (C/C for the same acrylonitrile concentration.

The fifth advantage of this invention consists in the fact that the highstability against the decomposition of the supporting electrolyte can beutilized for heating the catholyte and other solutions originatingtherefrom to hlgh temperatures for the purpose of isolatingadiponitrile.

The sixth advantage of this invention consists in the fact that the highspecific conductivity of the supporting electrolyte serves to reduce theconsumption of electriclty involved in the manufacture of hydrodimer.For example, a solution composed of 30% of tetraethylammonium sulfate,the supporting electrolyte used for this invention, 8% of acrylonitrileand 62% of water has a specific resistance of 269 cm. at 25 0, whereas amixed solution of 30% (corresponding to the concentration of theprevious solution) of tetraethylammonium p-toluenesulfonate, which is aquaternary ammonium salt used by the conventional known methods andwhich has the same alkyl group, 8% of acrylonitrile, and 62% of waterhas a specific resistance of 629 cm. at 25 C. The high specificconductivity of the supporting electrolyte of this invention can beexplained by reasoning that cations of this invention occurring from thedissociation of the supporting electrolyte have substantially the sameconductivity as those of the conventional known supporting electrolytewhereas anions of this invention are sulfate ion, which are smaller indimen sions and consequently higher in mobility than p-toluenesulfonateions or alkylsulfate ion of the conventional known method.

Especially, as the seventh advantage of this invention, the cellresistance is reduced remarkably and the selectivity of adiponitrile isincreased when the electrolysis is carried out by using a quaternaryammonium sulfate having an alkyl group of not more than three carbonatoms, with the concentration of this suppotring salt in the electrolytefixed below 40%. The reason is that the aqueous solution of quaternaryammonium salt of this invention shows its minimum specific resistance inthe salt concentration range of from 20 to 40% by weight. In the higherconcentration range of supporting salt, the specific conductivity islowered which increases the unit power consumption for the manufactureof adiponitrile and also increases the solubility of acrylonitrile,therefore, the production of adiponitrile cannot be accomplished in agood yield and consequently the purpose of this invention cannot beachieved unless the concentration of acrylonitrile should be increasedto a suitable range of C/C Such adjustment increases the powerconsumption again.

As described above, the method of this invention is effective in thatthe hydrodimerization of acrylonitrile can be accomplished in asubstantially high yield with small power consumption, and that thedimerization can be conducted while preventing the formation ofpropionitrile and harmful side reaction at the anode. Further, in thisinvention the process of separating the product and the raw material canbe simplified and recovery of the supporting electrolyte is simplified.

According to this invention, the catholyte is a solution which containsa quaternary ammonium sulfate, acrylonitrile, and water, with theconcentration of acrylonitrile ranging from 3 to 60% by weight, that ofwater corresponding to to 90% of the total weight of the catholyte, andthat of quaternary ammonium sulfate in the range of from 1 to 60%.Generally, with the increasing number of carbon atoms in the groupbonded to the nitrogen of quaternary ammonium sulfate, the solubility ofacrylonitrile in the catholyte is increased. For example, acrylonitrileis dissolved by about 8% by weight in the catholyte at 25 C. whichcontains 0 to 60% of tetraethylammonium sulfate. In the aqueous solutionof more than of tetrabutylammonium sulfate, acrylonitrile can bedissolved to form homogeneous solution at whatever concentration desiredat C.

In View of separating adiponitrile formed by electrolysis from a cathodecompartment efliuent, it is advantageous to use a quaternary ammoniumsalt of high affinity with water but comparatively less affinity withadiponitrile and acrylonitrile. It is, therefore, advantageous to employa quaternary ammonium compound such as tetramethylammonium sulfate ortetraethylarnmonium sulfate with a radical having less carbon atombonded to nitrogen. In conducting electrolysis using quaternary ammoniumsalt of comparatively less affinity with adiponitrile and acrylonitrileas stated above, it is easy to obtain a solution of adiponitrilecontaining less amount of supporting electrolyte by extracting thecathode compartment eflluent with an organic solvent. For example, inthe actual operation of electrolysis the efiiuent of cathode compartmentis received in a tank outside the electrolytic cell and the lower layeris drawn from the bottom of said tank to circulate to a cathodecompartment while feeding acrylonitrile to said tank or a cathodecompartment efiiuent. By doing so, the adiponitrile in the cathodecompartment eflluent is extracted with acrylonitrile added, and in thetank there are produced an oil layer consisting of adiponitrile andacrylonitrile as an upper layer and an aqueous layer mostly composed ofthe supporting electrolyte and water together with decreasedconcentration of adiponitrile due to extraction by acrylonitrile as alower layer. When this lower layer is supplied to the cathodecompartment and the electrolysis is continued, the adiponitrile formedby electrolysis is extracted by acrylonitrile and separated in the upperlayer of the tank. It is possible in this invention to obtain with easethe product containing less supporting electrolyte by drawing off theupper layer alone.

Use of a quaternary ammonium salt of this invention will not cause asubstantial increase of solubility of acrylonitrile beyond thesolubility of acrylonitrile in water.

Especially, in a special method wherein a quaternary ammonium salthaving alkyl group of less than three carbon atoms is used, thesolubility of acrylonitrile in the electrolyte is not substantiallyincreased due to the addition of supporting salt beyond that in thewater, and C/C representing a ratio of the concentration ofacrylonitrile in the catholyte for electrolysis C to a solubility ofacrylonitrile in the electrolyte C is easily adjusted to a suitablevalue near to 1, as compared with the case using a supportingelectrolyte which substantially increase a solubility of acrylonitrilebeyond that in the water.

Generally, in the electrodimerization, as C/C is in a suitable rangenear to 1, so a selectivity of acrylonitrile to adiponitrile is higher.Therefore, when a supporting electrolyte of quaternary ammonium sulfateof less solubility of acrylonitrile, having an alkyl group of less thanthree carbon atom is used, the selectivity of acrylonitrile toadiponitrile is high.

In the case where a part of the acrylonitrile in the electrolyte isreplaced by adiponitrile, it is particularly advantageous because ofless formation of oligomer of acrylonitrile such as trimer, tetramer,etc. The reason is that it is possible to adjust the amount ofacrylonitrile on the electrode surface and prevent a formation ofoligomer in an advantageous way because adiponitrile dissolves in theelectroylte in the same performance as that of acrylonitrile and thesolubility of the mixture of acrylonitrile and adiponitrile makes almostno change in terms of the value of weight percentage even if a part ofthe acrylonitrile is replaced by adiponitrile.

The special quaternary ammonimum salt having an alkyl group of not morethan three carbon atoms bonded to nitrogen, one of the optimumconditions of the present invention, is explained in detail as follows.

In case such aqueous solution of quaternary ammonium salt is used,minimum point of the specific resistivity of the electroylte is foundwith the increase of the concentration of salt while keeping the contentof acrylonitrile constant. As an example, a specific resistivity ofsupporting electrolyte solution and a solubility of acrylonitrile isillustrated hereinbelow. Following tables show the relation of thespecific resistivity of aqueous solution of supporting electroylte vs.the concentration of said salt and solubility of acrylonitrile in theaqueous solution at the definite concentration of salt. Even if therelation of the specific resistivity of aqueous electrolyte containingspecific amount of acrylonitrile is plotted against the concentration ofsupporting salt, the concentration of the supporting salt whichcorresponds to the minimum value of resistivity of the said electrolyteis not substantially changed.

TABLE 1 Specific resistivity of tetraethylamrnoniurn sulfate aqueoussolution (25 C.)

Solubility of acrylonitrile in 30% (weight) tetraethyl sulfate aqueoussolution Percent (weight): C. 8.0 40 6.0 20

Similarly, conventional electrolyte has the same tendency as shown inTable 2.

TABLEZ Specific resistivity of aqueous solution of tetraethylammoniump-toluenesulfonate.

Salt concentration Specific resistivity (percent weight) (ti-cm) 10 96Solubility of acrylonitrile in 35% (weight) solution Percent (weight):

As evident from the above, when an electrolysis is especially conductedby using a supporting electrolyte of quaternary ammonium cation havingan alkyl group of not more than three carbon atoms bonded to thenitrogen, and having sulfate as an anion, solubility of acrylonitrile isabout 10% in a range of salt concentration from 0 to ity. This valueshows substantially no increase of acrylonitrile solubility as comparedwith the solubility of acrylonitrile in water, 7.35% (weight) at C.,7.9% (weight) at C., and 9% (Weight) at 60 C.

Generally, electrolysis in such special conditions facilitates theformation of acrylonitrile oligomer (e.g. hydrotrimer and hydrotetramerof acrylonitrile) as the concentration of acrylonitrile approaches nearsaturation. Furthermore, a lower concentration of acrylonitrile thansaturation causes the formation of hydrogen gas, and leads to theformation of undesirable by-product propionitrile. Therefore, theoptimum point for an effective preparation of adiponitrile by usingquaternary ammonium having an alkyl group of not more than three carbonatoms, may be influenced by acrylonitrile concentration, current densityagitating condition on anode surface, temperature, etc., but generallythe optimum condition is in the range of about 3 to 10% acrylonitrileconcentration, if the concentration of supporting salt is defined tocover a lower range than the concentration corresponding to the minimumspecific resistivity of the electrolyte.

The temperature of electrolysis in the present invention can be at anydegree up to the boiling point of acrylonitrile, preferably in the rangeof 080 C. for better adjustment of solution and operation. The higherthe temperature, the greater the solubility of acrylonitrile. Thetemperature of the electrolysis, so long as it stays in the aforesaidrange, usually has no great influence upon the current efficiency andutilization of monomer for preparation of hydrodimer, but a highertemperature causes less electrolytic cell resistance and less powerconsumption.

Sometimes it is desirable to add a solvent to the anolyte for thepurpose of improving the current efliciency in the formation ofhydrodimer or the selectivity of acrylonitrile at the cathode, or forthe purpose of improving or controlling the solubility of acrylonitrileinto the catholyte.

It is sometimes desirable to add to the catholyte such solvents asacetonitrile, propionitrile, dioxane, dimethylformamide,dimethylsulfoxide, trimethylamine, dimethylamine and other amines whichare all solvents of high polarity. It is also sometimes effective to addsolvents, which are electron acceptors. For the purpose of preventingpolymer formation other than the hydrodimer in the cathode, it isdesirable to add a polymerization inhibitor thereto and, at the sametime, remove oxygen from acrylonitrile and/or the catholyte.

Among the salts which can be employed according to the invention,quaternary ammonium sulfates are generally suitable. Such salts can bealkyl quaternary ammonium salts, quaternary ammonium salts having alkyland aralkyl groups, quaternary ammonium salts having aryl and/or alkylgroups, heterocyclic quaternary ammonium salts and alkylalkanolquaternary ammonium salts. Of the above quaternary ammonium compoundshaving alkyl groups, those having methyl, ethyl, butyl, and/or propylgroups bonded to the nitrogen atom are the most convenient to use.Compounds of quaternary ammonium having the phenyl group and thenaphthyl group, are representative salts having aryl groups bonded to anitrogen atom, and salts having the benzyl group and the methylbenzylgroup are representative of the salts having aralkyl groups bonded tonitrogen. Typical of these quaternary ammonium compounds aretetramethylammonium sulfate, tetraethylammonium sulfate,trimethylethylammonium sulfate, triethylmethylammonium sulfate,tetrapropylammonium sulfate, tetrabutylammonium sulfate,trimethylethylammonium sulfate, methylpyridinium sulfate,ethylpyridinium sulfate, trimethylbenzylammonium sulfate,triethylbenzylammonium sulfate, trimethylaniline sulfate andtriethylaniline sulfate.

As to the cathode, it is desirable to use an electrode which has highhydrogen overvoltage in order to prevent hydrogen formation at thecathode. Generally, there may be used such metals as copper, lead, tinand mercury or alloys of such metals.

Current density employed for the electrolysis may be in the range offrom 1 and amperes/dm. As a result of electrolysis, acrylonitrile isconverted generally by 70 to 100% into adiponitrile, while a part of itmay undergo side reaction for forming propionitrile, oligomer ofacrylonitrile (such as hydrotrimer), or biscyanoethyl ether. It isnecessary to control the occurrence of these side reactions as far aspossible. Of said side reactions, the formation of propionitrile is easyto occur in the cathode compartment solution having a low pH value andin the electrolytic cell wherein the turbulence condition in the cathodecompartment is not so strong as the supply enough acrylonitrile to thecathode, and also oligomer is liable to occur when the acrylonitrileconcentration is high. Therefore, the concentration of acrylonitrile andthe pH of the cathode compartment should be selected so as to minimizethe yield of these side reactions. It is necessary, therefore, tomaintain the catholyte at such pH that the eflluent solution fromcathode compartment will have pH in the range of from 2 to 9.5, and itis proper to keep the concentration of acrylonitrile in the catholyte inthe order of from 3 to 40%. The side reactions at the cathode areinfluenced by the pH, monomer concentration, etc., on the surface of thecathode, therefore, it is necessary to make suitable arrangements sothat the electrolyte may be sutficiently agitated in the cell and on thesurface of the electrode and the concentration gradient of hydroxyl ionand acrylonitrile on the cathode may be reduced sulficiently. Toaccomplish this purpose, it is suitable to increase the flow velocity inthe cathode compartment or to insert a spacer (or separator) within thecathode compartment for creating turbulence flow by the collision of theflow with the spacer, or to use a spacer called tortuous path which isso designed that the fluid is passed through narrow channel at a highspeed and is caused to create turbulence due to collision againstobstacles placed between said channel to half the compartment width.Generally, the flow velocity suitable for this invention is in the rangeof from 0.1 to 200 cm./second, more desirably from 5 to 100 cm./second.

Sulfuric acid solution is used as an anolyte. The concentration ofsulfuric acid can be selected in the range of from 1 to 60%, it isproper generally to select it in the range of from 1 to 20% because thecorrosion of anode becomes heavier with the increasing sulfuric acidconcentration. As the material of anode, it is suitable to use platinum,nickel, nickel silicide, Duriron, lead, and lead alloys, particularlylead-antimony alloy.

As a cation exchange membrane, the ion-exchange membranes havingsulfonic acid groups and carboxyl groups can be used, the most suitablemembrane is the sulfonated styrene-divinylbenzene polymer. Such cationexchange membranes can be either homogeneous or heterogeneous. When acation exchange membrane is placed to separate the anode compartment andthe cathode compartment, the membrane selectively transfers hydrogenions from the anode compartment to the cathode compartment and, as aconsequence, the hydroxy ions produced at the cathode are neutralizedquantitatively, permitting the pH of the cathode compartment to bemaintained constant. It the electrolysis, the cation exchange membraneis desired to have ideal characteristics as to transfer only hydrogenions but prevent sulfate ion and other catholyte ingredient likeacrylonitrile from migration to anode compartment. In the case of thisinvention, however, even if anions of the supporting electrolyte in thecathode compartment migrate through the membrane in a small amount anddischarge at the anode, they will not induce harmful corrosion of theanode. When the pH of the cathode compartment is changed throughinsufficient neutralization, required neutralization can be accomplishedby adding any kind of acid from outside.

The present invention will be explained in the following examples,however, it should not be constructed that these examples restrict thepresent invention in any event, since they are given merely by way ofillustration:

EXAMPLE 1 The electrolytic cell was used, in which both the anode andcathode were of lead, the anode compartment and cathode compartment wasdivided by a cation exchange membrane of sulfonated 1 mm. thickdivinylbenzenestyrene-butadiene copolymer and the distance between themembrane and the electrode was 1 mm. As an anolyte, 0.5 N sulfuric acidsolution was circulated. The catholyte was circulated in the cathodecompartment at a flow velocity of 20 cm./sec. and electrolyzed at thetemperature of electrolyte of 40 C. The current density was amp./dm. forboth electrode.

During the electrolysis, the efiluent of cathode compartrnent wasseparated into two phases by adding acrylonitrile to the cathodeefiluent. When this solution stood for more than few minutes,adiponitrile formed at the cathode was extracted with acrylonitrile asthe upper oil phase. The lower phase was recirculated to the cathodecompartment. Tetrapropylammonium sulfate was used to support electrolytein catholyte.

During the electrolysis, the composition of the upper oil phase was60.7% of adiponitrile, 8% of oligomer, biscyanoethyl ether andropionitrile, 0.4% of supporting electrolyte, 24.6% of acrylonitrile and6% of water. Also, the composition of the lower phase was 6% ofacrylonitrile, 12% of supporting salt, the rest being water andelectrolytic products which were mainly adiponitrile and minor part ofpropionitrile, oligomer, biscyanoethyl ether and etc.

On the basis of the amount of acrylonitrile consumed in thiselectrolysis, the selectivity of electrolytic reaction was as follows:

Product: Selectivity, percent Adiponitrile 88.9 Propionitrile 7.7Oligomer 3.4 Biscyanoethyl ether 0.1

On the contrary, when the hitherto publicly known tetraethylammoniurnp-toluenesulfonate was used as supporting salt in lieu oftetrapropylammonium sulfate and this electrolyte was electrolyzed underthe same electrolytic conditions as the above, the concentration ofsupporting salt in the upper phase was 4% and the yield of adiponitrile83%.

EXAMPLE 2 An electrolytic cell was used, in which both the anode andcathode were of lead, the anode compartment and cathode compartment wasdivided by cation exchange membrane of sulfonated 1 mm. thickdivinylbenzenestyrene-butadiene copolymer and the distance between themembrane and electrode was 1 mm. As an anolyte, 0.5 N sulfuric acidsolution was circulated and the catholyte was circulated in the cathodecompartment at a flow velocity of 20 cm./sec. and electrolyzed at thetemperature of 30 C., the current density was 10 amp./dm. for bothelectrodes.

The catholyte in which, as supporting electrolyte, tetraethylammoniumsulfate was used, was electrolyzed for two hours while being controlledin the following composition.

Catholyte composition:

Acrylonitrile percent weight 5.0-6.0 Supporting salt do 10-9Electrolytic products and water do The rest pH 4 a-Naphthylamine(inhibitor) p.p.m 1,000

The electrolytic products were mainly adiponitrile and minor part ofpropionitrile, oligomer, biscyanoethyl ether and etc. On the basis ofthe amount of acrylonitrile consumed in this electrolysis, theselectivity of the electro lytic reaction was as follows:

Product: Selectivity, percent Adiponitrile 88.5 Propionitrile 6.4Oligomer 5.0 Biscyanoethyl ether 0.1

EXAMPLE 3 Acrylonitrile percent weight 6.0-7.0 Supporting electrolyte do29-30 Electrolytic products and water do The rest pH 8 a-Naphthylaminep.p.m 1,000

I On the basis of the amount of acrylonitrile consumed 111 thiselectrolysis, the selectivity of electrolytic reaction was as follows:

Product: Selectivity, percent Adiponitrile 78.0 Propionitrile 16.8Oligomer 5.0 Biscyanoethyl ether 0.2

EXAMPLE 4 The same electrolytic cell and anolyte as in the Example 2were used. The catholyte was circulated in the cathode compartment at aflow velocity of 60 cm./sec. and electrolyzed at a temperature of 30 C.The current density was 10 arnp./dm. for both electrodes. The catholyte,in which as a supporting salt diethylethanolbenzylammonium sulfate wasused, was electrolyzed for two hours while being controlled in thefollowing composition.

Catholyte composition:

Acrylonitrile percent weight-.. 6.0-7.0 Supporting electrolyte do 12-13Electrolytic product and water do The rest pH 8 a-Naphthylamine p.p.m1,000

1 1 On the basis of the amount of acrylonitrile consumed in thiselectrolysis, the selectivity of electrolytic reaction was as follows:

Product: Selectivity percent Adiponitrile 85.0 Propionitrile 6.2Oligomer 8.5 Biscyanoethyl ether 0.3

EXAMPLE 5 Catholyte composition:

Acrylonitrile percent weight 20 Supporting electrolyte do 19-20Dimethylformamide do 20 Electrolytic products and water do.. The rest pH7.2

a-Naphthylamine On the basis of the amount of acrylonitrile consumed inthis electrolysis, the selectivity of adiponitrile Was 83 In the aboveExamples 27, the oil phase of adiponitrile was enough low in the contentof supporting electrolyte and could be separated and extracted, as inthe case of the Example 1 by adding acrylonitrile to the solution at theeffluent of cathode compartment.

EXAMPLE 6 An electrolytic cell was used, in which both the anode andcathode are of lead, the anode compartment and cathode compartment aredivided by cation exchange membrane of sulfonated 1.mm..thickdivinylbenzenestyrene-butadiene copolymer, and the distance between themembrane and electrode was 1 mm. As an anolyte,

2 N sulfuric acid was circulated in the anode compartment. Thecatholytewas circulated in the cathode compartment at aflow velocity of20 cm./sec. and electrolyzed at a temperature at 40 C. The currentdensity was 10 amp./dm. for both electrodes.

The catholyte in which, as supporting salt, tetraethylammonium sulfatewas used, was electrolyzed for two hours while being controlled in thefollowing composition.

Catholyte composition:

Acrylonitrile percent weight 7.05.0 Supporting electrolyte do 19-21Electrolytic products and water do The rest pH 4 u-Naphthylamine p.p.m1,000

The electrolytic products were mainly adiponitrile and minor parts ofoligomer, biscyanoethyl ether and etc. On the basis of the amount ofacrylonitrile consumed in this electrolysis, the selectivityofelectrolytic reaction was as follows:

Product: Selectivity, percent Adiponitrile 88.9 'Propionitrile 7.6Oligomer 3.4 Biscyanoethyl ether 0.1

What is claimed is:

1. In a method of manufacturing adiponitrile by electrolyzing in adivided cell the catholyte of an aqueous solution comprisingacrylonitrile and quaternary ammonium sulfate having at least oneradical selected from the group consisting of alkyl, aryl and aralkylbonded to the nitrogen atom of said quaternary ammonium compound,sulfuric acid solution being used as an anolyte, and the anolyte beingseparated by a cation exchange membrane from the catholyte, theimprovement comprising using a concentration of dissolved acrylonitrilein said catholyte of from 3 to 10% by weight.

2. Method according to claim 1 in which the efiluent solution of thecathode compartment of said divided cell is separated into two phases byadding acrylonitrile to said efiluent to extract adiponitrile therefrom.

3. Method according to claim 1 in which said quaternary ammonium sulfatehas an alkyl radical of not more than three carbon atoms.

4. Method according to claim 1 in which said quaternary ammonium sulfatehas at least one alkyl radical of not more than three carbon atomsandthe concentration of said salt is kept at lower than that where thespecific resistivity of the cathlyte is minimum in relation to theconcentration of said salt.

5. Method according to: claim 1 in which said quaternary ammoniumsulfate is selected from the group consisting of tetramethylammoniumsulfate, tetraethylammoniurn sulfate, trimethylethylammonium sulfate,triethylmethylammonium sulfate and tetrapropylammonium sulfate.

6. Method according to claim 1 in which the sulfate provides solubilityof acrylonitrile not higher than that in water and adiponitrile isseparated from the effluent solution of cathode compartment.

7. Method according to claim 1 in which the sulfate provides solubilityof acrylonitrile in the catholyte substantially less than that in water,acrylonitrile is added to the efiluent solution of cathode compartmentand adiponitrile is extracted and separated from the upper phase at thephase separation tank outside of the electrolytic cell.

References Cited UNITED STATES PATENTS Re. 24,865 9/1960 Juda et al.20498 3,193,477 6/1965 Baizer 20473 3,193,480 6/1965 Baizer et al. 204733,193,481 6/1965 Baizer 204--73 3,267,131 8/1966 Campbell et al. 204--73HOWARD S. WILLIAMS, Primary Examiner H. M. FLOURNOY, Assistant Examiner

